Overcurrent protective device

ABSTRACT

An operating plate and a jumping plate are connected together at one end by an actuation plate which movably holds a movable contact of the jumping plate in place against a main contact of a stationary plate. A subcontact of said stationary plate is faced into contact with a contact portion of a spring contact plate. A thermally expandable wire is connected across the length of the operating plate to cause the actuation plate to release the jumping plate when a predetermined minimum current flows through the wire to break a circuit. A pushbutton is provided so that said contact portion of the spring contact plate can be forced into contact with said subcontact of the stationary plate when said pushbutton is depressed.

United States Patent Osawa 1 July 15, 1975 OVERCURRENT PROTECTIVE DEVICE Primary Examiner-Arthur T. Grimley [75] Inventor: Kazuo Osawa, Yokohama, Japan Attorney Agem or Firm-Burgess Ryan Wayne {73] Assignee: Micron Electric Co., Ltd., Japan ABSTRACT [22] Flled: 1973 An operating plate and a jumping plate are connected [21] Appl. No.: 418,028 together at one end by an actuation plate which movably holds a movable contact of the jumping plate in place against a main contact of a stationary plate. A [52] 11.8. CI 337/126, 337/140 subcomact of Said Stationary plate is faced into [51] Int. Cl. ..H01h 61/00 Contact with a Contact portion of a p g Contact [58] Field 0! Search 337/130, 131, 123, 126, l A h u d b] d 337/140 382 384 388 389 390 p ate. t erma y expan a e wire 15 connecte across the length of the operating plate to cause the actuation plate to release the jumping plate when a [56] References cued predetermined minimum current flows through the UNITED STATES PATENTS wire to break a circuit. A pushbutton is provided so 2,354,933 8/1944 Winborne 337/126 that said contact portion of the spring contact plate 31056.37] l0/19152 Bmekhuyse" H 337/126 can be forced into contact with said subcontact of the 3174,05 3/1965 Almassy 337/[40 X stationary plate when said pushbutton is depressed. 3.328.544 6/1967 Hancock 337/126 3 Claims, 4 Drawing Figures OVERCURRENT PROTECTIVE DEVICE BACKGROUND OF THE INVENTION The present invention relates to an overcurrent protective device of the type in which the position of an ac tuating plate interposed between an operating plate and a jumping plate is varied in response to the expansion of a thermally expandable wire caused when overcurrent flows therethrough, so that a removable contact fixed to the jumping plate is instantaneously disconnected from a stationary plate.

The most widely used overcurrent protective devices are fused. but they are melted as overcurrent flows so that they must be replaced with new ones. When a rated current of a fuse is in excess of a rated current of an electric circuit to be protected, the circuit is burnt by excessive current. In order to overcome the problems of the fuses. there have been devised and demonstrated various types of circuit breakers which automatically open a current circuit under an abnormal condition and manually close the circuit when the cause of an abnormal condition is removed. However they are generally very complex in construction and circuit breakers of a relatively small rated current are not reliable in operation.

SUMMARY OF THE INVENTION One of the objects of the present invention is there fore to provide an improved overcurrent protective device which is simple in construction and highly reliable in operation.

Another object of the present invention is to provide an improved overcurrent protective device which is extremely reliable in operation even under a relatively small overcurrent condition.

A further object of the present invention is to provide an improved overcurrent protective device which may break an electric circuit even when a pushbutton for closing the electric circuit is again erroneously depressed before a cause for overcurrent is completely removed.

The above and other objects. features and advan tages of the present invention will become more apparent from the following description of one preferred embodiment thereof taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a perspective view of an overcurrent protective device in accord with the present invention;

FIG. 2 is a side cross sectional view thereof;

FIG. 3 is a perspective view thereof with a protective casing removed; and

FIG. 4 is an exploded perspective view thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 4, an overcurrent protective device generally indicated by II) in accordance with the present invention has a base 11 made of synthetic resin and provided with a stock 12 fitted into a hole 15 of a first stationary terminal 14 and a through hole 13 into which is fitted a leg 16 0f the first stationary terminal 14. A center through hole 12a is formed through the stock 12 in order to insert a pin 17 therein. After the first stationary terminal 14 has been mounted with the leg 16 inserted into the hole 13 and the stock 12 fitted into the hole 15 of the first stationary terminal 14, through holes 18a. I90, 20:! and 21a of an insulating plate 18, a jumping plate 19, an operating plate 20 and a score washer 21 are fitted in the order named over the pin 17 fitted into the through hole 12a of the stock 12. Thereafter the pin I7 is caulked to hold the insulating plate 18, the jumping plate 19. the operating plate 20 and the score washer 21 securely in position.

The end 19!; of the jumping plate 19 remote from the through hole 19a is folded back in the form of an in verted U-shape. and the folded back portion is provided with a through hole 19(' into which is fitted one corner 22b ofa square actuating plate 22 (See FIG. 3). The end 20b of the operating plate 20 remote from the through hole 200 is bent upright and provided with a hole 20c in the form of a club into which is fitted another corner 22a of the square actuating plate 22 in such a way that the square actuating plate 22 may be interposed between the inverse U-shaped end 1911 of the jumping plate 19 and the upright end 20!; of the operating plate 20 (See FIG. 3). At the base of the upright end 20!) of the operating plate 20 is formed a through hole 20d into which is fitted one end 23b of a thermal expansion wire 23 so as to be securely held to the oper ating plate 20. The other end 231: of the thermal expansion wire 23 is securely held to a projection 14b of the upright portion of the first stationary terminal I4. (See FIGS. 2 and 3). Therefore the thermal expansion wire 23 causes the operating plate 20 to move upwardly.

The jumping plate I9 is made ofa relatively soft elastic material. whereas the operating plate 20 is made of a relatively hard elastic material. When the thermal expansion wire 23 is cold so that its length is short. the operating plate 20 is bent upwardly by the thermal expansion wire 23. Therefore when the inverted U-shaped end 19b of the jumping plate I9 is pushed down. the jumping plate 19 is moved downwardly to incline the square actuating plate 22 so that the jumping plate 19 remains bent downwardly. When the wire 23 expands. the upright end 2011 of the operating plate 20 is displaced downwardly and when the actuating plate 22 becomes in parallel with the base II, the pressure which is pushing the end 19b of the jumping plate 19 is released so that the end 19!; instantaneously jumps upwardly. A removable contact 24 is fixed to the undersurface of the jumping plate 19 close to its root of the inverted U-shaped end 19b. Legs 25!) of a stationary plate 25 are inserted into holes 26 formed in the base 11 and caulked so that a main contact 25a of the stationary plate 25 may be in opposed relation with the contact 24. The subcontact 25c of the stationary plate 25 is made into contact with the upper surface of a folded-back portion 27a of a spring contact plate 27. Fins 27b are formed integral with the folded-back portion 270. One leg 28a of a second stationary terminal 28 is fitted into a hole 27d formed through the end portion 27c of the spring contact plate 27 and also fitted into a through hole 29 formed through the base 11 and caulked to securely hold the second stationary terminal 28 and the spring contact plate 27 to the base II. The other leg 28b of the stationary terminal 28 is inserted through a through hole 30 formed through the base II and connected to a lead wire which in turn is connected to an electric circuit.

A protective casing 32 is fitted to the peripheral projecting portion 31 of the base 1 l, and the legs 33 of the protective casing 32 are snuggly fitted into mating recesses 34 formed in the periphery of the base 11 and caulked to securely assemble the protective casing 32 with the base 11. The protective casing 32 is also provided with projections 320 which may be used to mount the overcurrent protective device upon a distribution switchboard or the like (not shown).

A pushbutton 35, which is slidably fitted into a hole formed through the top of the casing 32, is normally biased to move upwardly under the force of a leaf spring 36 which is securely fixed to the undersurface of the top of the casing 32 by a fixed member 360. The pushbutton 35 is provided with bifurcated arms 37 which sandwich the jumping plate l9 and the operating plate and a lever-like extension 38 which extends at a right angle to the axis of the pushbutton 35. A pair of projections 39 are formed to extend from the inner surface of one side wall of the casing 32 so as to permit only the vertical movement of the bifurcated arms 37 and hence the pushbutton 35 (See FIG. 2).

Next the mode of operation of the overcurrent protective device with above construction will be described hereinafter. When a rated current is flowing through the overcurrent protective device 10, the de' vice is in the state shown in FIG. 2. That is, the current flows from the leg 16 of the stationary terminal 14, through the upright portion 140, the thermal expansion wire 23, the operating plate 20, the jumping plate 19, the movable plate 24, the stationary contact 25, the spring contact plate 27 and the terminal 28 to the leg 28h thereof. When excessive current flows, the thermal expansion wire 23 expands itself so that the operating plate 20 is caused to bend itself downwardly. When the actuating plate 22 becomes in parallel with the base 11, the inverted U-shaped end 191) of the jumping plate 19 suddenly jumps upwardly so that the contact 24 is instantaneously made out of contact with the stationary plate 25, thereby interrupting the current. When the excessive current does not flow so that the expansion wire 23 returns to its normal length. the operator pushes the pushbutton 35. The extension 38 of the pushbutton 35 pushes downwardly the inverted U- shaped end 19b of the jumping plate 19 so that the removable contact 24 is made into contact with the main stationary contact 25:: of the plate 25 again as shown in FIG. 3. The arms 37 push the fins 27b of the spring contact plate 27 to make the contact portion 27a thereof out of contact with the subcontact 25c. thus interrupting the current flow when the thermal expansion wire 23 has not yet completely returned to its initial length or condition. Therefore the erratic operation may be completely prevented even when the pushbutton 35 is depressed before the cause of excessive current has been completely removed.

What is claimed is:

1. An overcurrent preventive device comprising a. a first stationary terminal fixed to a base,

b. a jumping plate one end of which is securely fixed to said first stationary terminal,

c. an operating plate one end of which is securely fixed to said first stationary terminal,

d. a thermal expansion wire extending between an upright portion of said first stationary terminal and the other end of said operating plate.

e. an actuating plate fitted into a hole formed through the other end of said operating plate and into a hole formed through the other end of said jumping plate which is folded back in the form of an inverted U- shape,

f. a movable contact securely fixed to the undersurface of said jumping plate,

g. a main contact of a stationary plate made into contact with said movable contact,

h. a second stationary terminal electrically connected to said stationary plate fixed to said base, and whereby when excessive current flows through said thermal expansion wire said jumping plate instantaneously jumps upward to make said movable contact out of contact with said main contact of said stationary plate thereby interrupting overcurrent.

2. An overcurrent protective device as defined in claim 1 further comprising a pushbutton provided with a lever-like extension means for pushing downwardly the top of said inverted U-shaped end of said jumping plate when said pushbutton is depressed after said removable contact upon said jumping plate is made out of contact with said main contact of said stationary plate.

3. An overcurrent protective device as defined in claim 2 wherein said pushbutton is provided with a pair of bifurcated arms and fin portions formed integral with a contact portion of a spring contact plate which spring contact plate is electrically connected to said stationary contact and to said second terminal. said bifurcated arms contacting and pushing downwardly said fin portions when said pushbutton is depressed so that said contact portion of said spring contact plate is made out of contact with said stationary plate. thereby interrupting the overcurrent even when said pushbutton is depressed while the overcurrent flows through said overcurrent protective device. 

1. An overcurrent preventive device comprising a. a first stationary terminal fixed to a base, b. a jumping plate one end of which is securely fixed to said first stationary terminal, c. an operating plate one end of which is securely fixed to said first stationary terminal, d. a thermal expansion wire extending between an upright portion of said first stationary terminal and the other end of said operating plate, e. an actuating plate fitted into a hole formed through the other end of said operating plate and into a hole formed through the other end of said jumping plate which is folded back in the form of an inverted U-shape, f. a movable contact securely fixed to the undersurface of said jumping plate, g. a main contact of a stationary plate made into contact with said movable contact, h. a second stationary terminal electrically connected to said stationary plate fixed to said base, and whereby when excessive current flows through said thermal expansion wire said jumping plate instantaneously jumps upward to make saiD movable contact out of contact with said main contact of said stationary plate thereby interrupting overcurrent.
 2. An overcurrent protective device as defined in claim 1 further comprising a pushbutton provided with a lever-like extension means for pushing downwardly the top of said inverted U-shaped end of said jumping plate when said pushbutton is depressed after said removable contact upon said jumping plate is made out of contact with said main contact of said stationary plate.
 3. An overcurrent protective device as defined in claim 2 wherein said pushbutton is provided with a pair of bifurcated arms and fin portions formed integral with a contact portion of a spring contact plate which spring contact plate is electrically connected to said stationary contact and to said second terminal, said bifurcated arms contacting and pushing downwardly said fin portions when said pushbutton is depressed so that said contact portion of said spring contact plate is made out of contact with said stationary plate, thereby interrupting the overcurrent even when said pushbutton is depressed while the overcurrent flows through said overcurrent protective device. 